Before diving into tests and faults, you need to know what's inside a transformer's enclosure. In its basic form, a transformer consists of four elements, and a complete set of accessories is added in an oil-filled transformer.
The Basic Components
| Component | Function | Practical Note |
|---|---|---|
| Primary winding | Receives the supply from the source | Its number of turns determines one side of the turns ratio |
| Secondary winding | Delivers the required voltage to the load | Completely isolated from the primary |
| Iron core | Conducts the magnetic flux between the two windings | Insulated laminations to reduce eddy currents |
| Insulation | Prevents contact and electrical leakage | Affected by moisture and heat — the most important inspection point |
Accessories of an Oil-Filled Transformer
- Conservator tank: accommodates the expansion and contraction of the oil with temperature.
- Breather and silica gel unit: dries the air entering the tank.
- Buchholz relay: protection against internal faults that generate gases.
- Radiators and fans: dissipate heat to the surrounding air.
- Bushings: safely bring conductors in and out through the tank wall.
- Indicating instruments: temperature, pressure, oil level, and tap changer.
Remember the logical order: windings carry the power, the core conducts the flux, insulation protects, and accessories cool, monitor, and protect. Most transformer faults can be traced back to one of these four elements.
Sample answer: The primary winding receives the supply, the secondary winding delivers the voltage to the load, the iron core made of insulated laminations conducts the magnetic flux between the two windings, and the insulation prevents contact between the windings and between them and the body. In an oil-filled transformer, oil, the tank, the conservator tank, the breather unit, and protection and monitoring devices are added.
Neglecting to mention insulation as a basic component. Insulation is not a minor detail; most serious transformer faults begin with insulation deterioration caused by heat or moisture.
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